According to the state of the technology, automatic transmissions, especially for motor vehicles, include planetary sets which can be shifted by way of friction or shift elements, like clutches and brakes, and are usually associated with a starting element subject to a slippage effect and optionally with a bridge clutch, like a hydro-dynamic torque converter or a fluid coupling.
Such a transmission is known from EP 0 434 525 A1. It basically includes a drive shaft and an output shaft which are placed parallel to each other, a main gear set that is positioned concentrically to the output shaft and constructed as a double web, four shaft, planetary transmission and connectable to the drive shaft, an upstream gear set connected to the drive shaft and connectable to the main gear set, as well as five shift elements in the form of three clutches and two brakes whose selective blocking in pairs determines the various gear translations between the drive shaft and the output shaft. In the process, the transmission manifests two power paths so that six forward gears can be obtained by a selective engagement in pairs of the five shift elements.
In the process, two clutches are needed to transfer the torque from the upstream gear set to the two elements of the main gear set. These are basically positioned in the direction of power flow behind the upstream gear set in the direction of the main gear set. Another clutch is provided in the second power path which connects it in a disengageable manner with another element of the main gear set. In the process the two clutches are so positioned that the interior disc carrier forms the output.
In addition, a compact multispeed transmission of a planetary design, in particular for motor vehicles, is known from U.S. Pat. No. 6,139,463 which manifests two planetary gear sets coupled to each other and an upstream gear set, as well as three clutches and two brakes. In this known multispeed transmission, two clutches C-1 and C-3 are provided in the first power path to transfer the torque from the upstream gear set to both coupled planetary gear sets. In the process, the outer disc carrier or the cylinder or the pistons and the pressure compensation side of clutch C-3 are connected with a first brake B-1. In addition, the interior disc carrier of the third clutch C-3 is connected with the cylinder or the piston and the pressure compensation side of the first clutch C-1, where the interior disc carrier of the first clutch C-1 is placed on the output side and is connected with a sun gear of the third planetary gear set.
In addition, a multispeed transmission is known from DE 199 49 507 A1 from this Applicant, in which two non-shifting upstream gear sets are provided on the drive shaft which produce two rotational speeds on the output side that, in addition to the rotational speed of the drive shaft, are able to be engaged and disengaged on a multi-member shiftable main planetary gear set acting on the output shaft by way of selective engagement of the shifting elements used in such a way that to shift from one gear to the next higher or lower gear only one shift element of the two activated shift elements must be engaged or disengaged.
An automatic shifting motor vehicle transmission with three planetary gearsets as well as three brakes and two clutches for shifting six forward and one reverse gear and with a drive shaft and output shaft is known from DE 199 12 480 A1. The automatic shifting motor vehicle transmission is so constructed that the drive shaft is directly connected with the sun gear of the second planetary set and the output shaft is connectable with the sun gear of the first planetary set via the first clutch and/or the carrier of the first planetary set via the second clutch. Additionally or alternatively, the sun gear of the first planetary set is connectable, via the first brake, with the housing of the transmission and/or the carrier of the first planetary set, via the second brake, with the housing and/or the sun gear of the third planetary set, via the third brake, with the housing.
From DE 102 13 820 A1, a multiple gear automatic transmission is also known and includes an initial input path T1 with an initial transmission ratio, an input path T2 which has a larger transmission ratio than input path T1, a planetary gear set with four elements, where the four elements are a first element, a second element, a third element and a fourth element in the sequence of elements in a rotational speed diagram, a clutch C-2 which conveys the rotation of the input path T2 to the first element S3, a clutch C-1 which transfers the rotation of input path T2 to the fourth element S2, a clutch C-4 which conveys a rotation of input path T1 to the first element, a clutch C-3 which transfers the rotation of input path T1 to the second element C3, a brake B-1 which engages the fourth element, a brake B-2 which engages the second element and an output element which is coupled to the third element R3.
In the context of the applicant's DE 101 15 983 A1, a multispeed transmission is described with a drive shaft which is coupled to the upstream set with an output shaft, which is connected to a set connected downstream, and with a maximum of seven shift elements by way of whose selective shifting at least seven forward gears can be selected without a compound transmission. The upstream set is formed from an upstream planetary gear set or a maximum of two non-shiftable upstream planetary gear sets coupled with the first upstream planetary gear set, where the set connected downstream is constructed as a two-carrier, four shaft gear with two shiftable planetary gear sets connected downstream and manifests four shafts. The first free shaft of this two-carrier, four shaft transmission is connected with the first shift element, the second free shaft with the second and third shift elements, the third free shaft with the fourth and fifth shift elements and the fourth free shaft is connected with the output shaft. For a multispeed transmission with a total of six shift elements, it is recommended in the invention that the third free shaft or the first free shaft of the set connected downstream also be connected with a sixth shift element. For a multispeed transmission with a total of seven shift elements, it is recommended in the invention that the third free shaft also be connected with a sixth shift element (D′) and the first free shaft also with a seventh shift element.
In addition, in the Applicant's DE 101 15 987, a multispeed transmission with eight gears is described. This transmission consists of a shiftable upstream gear set and a shiftable gear set connected downstream in addition to a drive shaft and an output shaft. The upstream gear set consists of a first planetary gear set which offers, in addition to the input rotational speed of the drive shaft, a second rotational speed which can selectively be switched to the gear set connected downstream. The gear set connected downstream consists of two coupled planetary gear sets. By using two power paths and six shift elements, eight forward gears can be shifted without a compound transmission. An 8 gear multispeed transmission is also known from DE 29 36 969; it includes eight shift elements and four gear sets.
A multispeed transmission is also known from U.S. Pat. No. 6,716,131 B1 which includes three coupled minus-planetary gear sets, three clutches and two brakes. These transmissions can be constructed as 5 gear, 6 gear and 7 gear transmissions, where one element of one of the planetary sets is permanently connected with the housing to prevent rotation so that the transmission manifests six rotating shafts.
In general, automatically shifting vehicle transmissions with a planetary design have already been described extensively in the state of the technology and are subjected to constant further development and improvement. These transmissions should thus have a sufficient number of forward gears as well as a reverse gear and a transmission ratio well suited for vehicles with a high overall spread of gear ratios as well as favorable progressive ratios. In addition, it should enable a high starting transmission ratio in the forward direction and contain a direct gear as well as being suitable for use in both cars and commercial vehicles. Moreover, this transmission should require a low construction cost and, in particular, a small number of shift elements and avoid so-called compound transmission shifts during sequential shifting so that, when shifting from one gear to the next higher or the next lower gear, only one previously engaged shift element is opened and only one previously not selected shift element is engaged.
This invention has the goal of proposing a multispeed transmission of the type specified above in which the construction cost is optimized and, in addition, the degree of effectiveness is improved in the main drive gears in terms of drag and gearing losses. In addition, according to this invention, in the multi-stage transmission the torque acting on the shift elements and planetary sets should be limited and the rotational speed of the shafts, shift elements and planetary sets should be kept as low as possible. Additionally, the number of gears and the spread of gear ratios should be increased so that at least eight forward gears and at least one reverse gear are advantageously obtainable. In addition, according to this invention, the transmission should be suitable for installation in any configuration in any vehicle, especially for a front-transverse arrangement.